The present invention relates to apparatus and method for producing low emission of hydrocarbon, carbon monoxide and nitrous oxide in spark ignition gasoline engines, particularly for use in automotive vehicles and trucks.
The present invention discloses method and apparatus for achieving such low emission through the development of what is commonly termed a stratified charge, i.e., wherein the gasoline and air are introduced into the combustion area in a stratified form whereby a fuel-rich portion is essentially segregated from a second portion which is essentially air, and such stratification is preserved until ignition. Using the method and apparatus as disclosed herein, it is possible to achieve combustion using air-fuel ratios in excess of 24:1 which, in turn, produces exceedingly low emissions of the type mentioned. The method and apparatus, therefore, enable a manufacturer to produce gasoline powered engines which meet the low emission criteria established by the U.S. Federal Government and other governments for the purpose of reducing air pollution.
Stratified charge engines are not, per se, new. Perhaps the best known and certainly the most successful such engine on the U.S. Market today is that manufactured by the Honda Company and installed in its model CVCC 4-stroke spark ignition engine, which is believed to be substantially according to Honda U.S. Pat. No. 3,890,942.
The Honda engine employs two inlet valves to admit lean and rich air-fuel mixtures from two separate carborators to the cylinder. The cylinder head of the Honda engine has a recess to accomodate the inlet valve for the rich mixture, and is so shaped as to keep the rich mixture from being completely mixed with the lean mixture outside the recess and in the cylinder. Thus, two separate pockets of lean and rich mixtures are formed at the end of the compression stroke when the rich mixture inside the recess is ignited by a spark plug. When the rich mixture is being burned during the expansion stroke, the lean mixture outside the recess will also be burned when the flame front reaches it. The entry of lean mixture into combustion after the ignition of rich mixture by the spark plug promotes complete combustion and reduces air pollution.
The novelty of the Honda engine apparently is the combination of the following features:
1. One additional inlet valve, PA1 2. One additional carborator, and PA1 3. One separate recess in the cylinder head to keep the lean mixture from being completely mixed with the rich mixture before ignition takes place. PA1 1. It is more expensive because of the additional inlet valve and its related mechanism. PA1 2. It is more expensive because of the additional carborator. PA1 3. As compared with the simple hemispherical cylinder head of a conventional engine, the recess cylinder head of the Honda engine has larger surface area to lose heat and thus reduce efficiency. Also the length of the flame path from the spark plug to the remotest point of the cylinder head is longer, and thus the tendency of detonation is larger with the Honda engine. PA1 1. The engine must have reasonably high speed. PA1 2. The speed of gas or air flow must be well below the speed of sound so as to avoid choke due to shock wave. PA1 3. A gasoline injector cannot have high injecting pressure because of the low viscosity of gasoline, and thus the penetration of gasoline droplets into the engine cylinder is limited. Also, the droplets will spread like a cone instead of being coherent to one another. Furthermore, the injector must not be overheated such that the gasoline causes vapor lock. PA1 4. There has to be effective segregation between the rich and the lean parts of the air-fuel mixture at the instant of ignition. PA1 5. The manufacturing and operating cost must be reasonable.
The disadvantages of the Honda engine as compared with conventional 4-stroke spark ignition engines include the following:
Other inventors have attempted to produce low emission engines, but all such developments have certain substantial practical difficulties.
For example, Hallberg U.S. Pat. No. 3,079,901 granted Mar. 5, 1963 discloses a piston having an irregularly shaped top which form pockets when the piston is at top dead center. A fuel injector is provided at the top of the cylinder to inject fuel downward into one of the pockets. The difficulty with the Hallberg device, however, is that stratification of the air and fuel cannot really be achieved to a significant degree. This is because the fuel eminating from the fuel injector follows a cone-shaped path which sweeps through the cylinder in an axial direction and the fuel is carried away in the radial direction because turbulence due to the intake stroke is strong in the radial direction and weak in the axial direction. This means that stratification is very poor. Moreover, the Hallberg device could not operate at the high engine speeds necessary for modern use because the fuel would not be adequately positioned in the pocket intended by the Hallberg device at high speeds.
Moreover, in Hallberg, the irregularly shaped piston top will produce a hotter piston temperature and therefore a lower compression ratio. This, in turn, will require a higher octane fuel. As will be seen, the present invention utilizes in its preferred from a piston having an essentially flat top which in turn means that the piston will be cooler in operation and, therefore, the compression ratio can be higher and lower octane fuel can be used.
Finally, in Hallberg, the fuel injector is located directly in the combustion chamber which becomes hot during operation and is under high pressure during the beginning of the expansion stroke. This requires a very expensive type of fuel injector. On the other hand, as will be seen, the present invention utilizes one or more fuel injectors which operate in cool locations under relatively low pressure even during expansion stroke and therefore much less expensive injectors can be used.
Other prior art attempts to produce a successful stratified charge engine have been unsuccessful for a variety of reasons. For example, they do not satisfy the following necessary requirements:
The present invention, however, has been proven successful in actual operation. That is, an engine of 1500 cubic centimeter piston displacement constructed according to the present invention has operated at a speed of 3000 revolutions per minute with air-fuel ratios in excess of 24:1 producing extremely low emissions of hydrocarbons (less than 200 ppm), carbon dioxide (less than 8.6%), carbon monoxide (less than 0.01%), and proportionate traces of nitrous oxide. Since the air-fuel ratio required to meet the ultimate requirements for such gases by the U.S. Environmental Protection Agency requires an engine which can operate at approximately 15:1 air-fuel ratio of higher, the present invention is capable of operating well within the ultimate requirements imposed by such agency.
In general, it has been discovered by the present inventor that very high air-fuel ratios can be achieved by constructing an engine having a main combustion chamber and an auxiliary combustion chamber connected by a constricted throat. The main combustion chamber is the area above the piston top and bounded in part by the constricted throat. The auxiliary combustion chamber is fixed (i.e. is not part of the piston) to the engine frame.
In the present invention, gasoline maybe injected through a fuel injector from a port in the cylinder wall at or near bottom dead center (B.D.C.), and the port itself may be at or near B.D.C. or may be somewhat higher up the cylinder wall. The gasoline thus injected forms a layer of rich fuel in the main combustion chamber directly above the piston. Air is introduced in such a way as to be positioned in the auxiliary combustion chamber and a spark plug is positioned so as to ignite the rich fuel pocket in the main combustion chamber.
The fuel may be injected either at or near bottom dead center or through the intake valve as, for example, by means of injection into the intake manifold. In the latter case, a charge of fuel is injected before air is introduced into the manifold so that the charge of fuel forms a rich fuel parcel behind the stem of the intake valve and the air forms a rich air parcel behind the rich fuel parcel, thus forming a stratified configuration. This stratification is maintained when the intake valve is opened because the diffusion of turbulence in a unidirectional flow of fluid is strong in the direction perpendicular to the flow and weak in the direction of the flow. Thus, as the fuel and air parcels enter the cylinder as the piston descends during the intake stroke, the stratification is preserved in the axial direction although the parcels tend to diffuse in a horizontal direction to some degree. Similarly, when the piston rises on the compression stroke, stratification is preserved in the axial direction.
It is possible, in the present invention, to use one or more fuel injectors located in the cylinder wall and one or more fuel injectors located behind the intake valve.
The main combustion chamber, as noted, communicates with an auxiliary combustion chamber through a constricted throat. Thus, when the stratified air and fuel parcels are pushed upward in the cylinder as the piston rises and the air rich portion passes through the constricted throat into the auxiliary chamber, while the rich parcel of fuel is concentrated in the main combustion chamber and around the electrodes of the spark plug or spark plugs, thus providing a rich mixture for ignition. The foregoing and other advantages of the present invention will become apparent from the following description and from the drawings.